1. Field of the Invention
The present invention relates to novel polymer compositions and methods for using such compositions. In general terms, the polymer compositions of the present invention are believed to be useful in water treatment in paper manufacture and as a rheology modifier.
2. Brief Description of the Prior Art
An interpenetrating polymer network (“IPN”), is an intimate combination of two polymers, both in network form, at least one of which is synthesized in the immediate presence of the other. In an IPN, at least one of the two polymers is crosslinked and the other may be a linear polymer (not crosslinked). The term IPN has been variously used to describe materials where the two polymers in the mixture are not necessarily bound together, but the components are physically associated.
U.S. Pat. No. 5,925,379 to Mandeville, III et al. discloses a method for removing bile salts from a patient, where a polymer network composition, which includes a cationic polymer is administered to the patient. The polymer network composition can include an interpenetrating polymer network, where each polymer within the network is crosslinked or an interpenetrating polymer network, where at least one polymer within the network is not crosslinked. Crosslinking the polymers renders the polymers non-adsorbable and stable. The polymer network composition does not dissolve or otherwise decompose to form potentially harmful byproducts and remains substantially intact so that it can transport ions out of the body following binding of bile acids.
U.S. Pat. No. 5,693,034 to Buscemi et al. discloses an angioplasty catheter that includes a composition coating on a distal end. The coating composition includes the reaction product of vinyl monomers polymerized to form a crosslinked polymer that adheres to the surface of the device in the presence of an uncrosslinked linear, water-soluble, hydrophilic hydrogel.
U.S. Pat. No. 5,644,049 to Giusti et al. discloses a biomaterial that includes an IPN. The IPN includes an acidic polysaccharide, such as hyaluronic acid and a non-toxic, non-carcinogenic synthetic polymer. The synthetic polymer may be crosslinked or grafted onto the acidic polysaccharide. The crosslinking or grafting is achieved using compounds capable of generating radicals or via functional groups on the acidic polysaccharide and the synthetic chemical polymer.
As the IPN examples described above illustrate, an IPN includes at least one crosslinked polymer with one or more other polymers, which may or may not be crosslinked in intimate combination with each other. When water-soluble polymers are included in the IPN, the resulting IPN is water dispersible, but it does not dissolve in water. While the use of an IPN may provide useful combinations of properties, its water insolubility can be a detriment in many end use applications.
U.S. Pat. No. 4,028,290 to Reid discloses a complex mixture of crosslinked grafted polysaccharide and acrylamide copolymers that have increased water-absorbing and binding capacity. The copolymers are prepared by reacting a polysaccharide, such as cellulose or starch, with acrylamide using a bisulfite-persulfate-ferrous ammonium sulfate grafting initiator.
U.S. Pat. No. 4,703,801 to Fry et al. discloses a graft polymer that has a backbone derived from lignin, lignite, derivatized cellulose, or synthetic polymers, such as polyvinyl alcohol, polyethylene oxide, polypropylene oxide, and polyethyleneimine, and pendant grafted groups that include homopolymers and copolymers of 2-acrylamido-2-methylpropanesulfonic acid, acrylonitrile, N,N-dimethylacrylamide, acrylic acid, N,N-dialkylaminoethylmethacrylate, and their salts. The graft copolymers are prepared by reacting the backbone polymer with ceric salts and a persulfate-bisulfite redox system in the presence of the selected monomers. The graft copolymers are useful in cementing compositions for use in oil, gas, water, and other well cementing operations and impart improved fluid loss capabilities.
U.S. Pat. No. 4,464,523 to Neigel et al. discloses graft copolymers of cellulose derivatives and N,N-diallyl,N-N-dialkyl ammonium chlorides or bromides, prepared using a dry or substantially solvent-free system. The preparation includes impregnating a concentrated aqueous solution of the N,N-diallyl-N,N-dialkyl ammonium halide, water-soluble surfactant, and redox catalyst onto the dry cellulose substrate, heating the reaction mass for sufficient time to achieve polymerization and then drying.
As described above, graft copolymers of polysaccharide and cellulosic backbone polymers are generally prepared by reacting portions of the backbone polymer with a redox catalyst generally including a ceric or ferrous salt to generate one or more free radicals. The free radicals on the backbone polymer then react with the monomers that are present to literally grow in graft polymer from the backbone polymer.
Graft copolymers differ from IPNs in that a first polymer acts as a substrate onto which another polymer is added, or a site on the first polymer is involved in initiating polymerization to form a pendant polymer arm. Graft copolymers can readily be formed from polysaccharide or cellulosic backbones using methods well known in the art. Examples of such methods include the ceric salt redox method (U.S. Pat. No. 3,770,673 to Slagle et al.) and graft initiation using formaldehyde and sodium metabisulfite (U.S. Pat. No. 4,105,605 to Cottrell et al.). In order to achieve a high degree of grafting, heavy metal ions, such as cerium IV or ferrous, or reagents, such as formaldehyde, are used to augment the grafting reaction. In many cases, the presence of such materials in a copolymer is undesirable because they are considered by many to be cancer causing agents in humans as well as environmentally harmful.
Further, graft copolymers are limited in the functional properties that they can provide. For example, the graft copolymer of U.S. Pat. No. 4,464,523 to Neigel et al. has highly charged cationic arms and a neutral backbone. The possible polymer confirmations that allow such a polymer to interact with a substrate are limited compared to a linear polymer. This limitation results in inferior performance when such a polymer is required to adsorb onto a substrate, for example, in waste water treatment or paper making applications.
Mixtures of polymers have been used in waste water treatment applications. For example, U.S. Pat. No. 4,699,951 to Allenson et al. discloses a polymer admixture that includes a low molecular weight cationic polymer and a high molecular weight cationic copolymer of acrylamide for treating and clarifying waste waters contaminated with oily waste and dispersed solids. U.S. Pat. No. 5,213,693 to McGrow et al. discloses treating sewage sludge and other organic suspensions for filter press or belt press dewatering using a dry blend of a low molecular weight cationic polymer and a high molecular weight cationic copolymer of acrylamide. U.S. Pat. No. 5,624,570 to Hassick discloses a method for treating laundry waste by sequentially adding a low molecular weight cationic polymer and a high molecular weight cationic copolymer of acrylamide to the waste stream. U.S. Pat. No. 5,906,750 to Haase discloses a method for the dewatering of biological sludge that has been digested by a thermophilic digestion process that includes sequentially adding a low molecular weight cationic polymer and a high molecular weight cationic copolymer of acrylamide to the biological sludge.
Unfortunately, physical mixtures of low molecular weight cationic polymers and high molecular weight cationic copolymers of acrylamide are not stable over time, as they tend to separate into two phases. Dry blends of such polymers are also problematic in that they are difficult to make down into a solution and readily adsorb moisture, which leads to clumping of the dry powder.
As the above examples demonstrate, however, in many uses for water-soluble polymers, it is desirable for the water-soluble polymer to adsorb onto a suspended solid surface from an aqueous solution to neutralize the surface charge, promote coagulation and/or flocculation of the solids, or to stabilize the suspension. Because an IPN is a water insoluble material, it is not able to provide these types of polymer-surface interations. Further, graft copolymers do not provide adequate performance in such applications, and physical blends of polymers often lack the requisite shelf life required to be useful commercially.
It would, therefore, be desirable to provide a material that is able to combine the favorable properties of two or more polymers, without resorting to the formation of a crosslinked matrix. Such a material should be easily prepared, easily used, and stable, i.e., not separate over time.